Present network designs often provide for redundant processors in each network element. For example, redundant processors are to be provided for synchronous optical network (SONET) elements with only one processor active for communicating on a local area network (LAN) via a single, thin wire Ethernet connector.
The known ANSI IEEE standard 802.3 ISO/IEC 8802-3 entitled "Information Processing Systems-Local Area Networks---Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications" specifies typical requirements. Such specifications deal with several types of interconnections including "10 base 2, 10 base 5, 10 base T," etc. The 10 base 2 specification deals with thin wire coaxial Ethernet local area networks operating at 10 megabits per second with a maximum span of 185 meters. The other two above-mentioned specifications deal with thick coax up to 500 meters (10 base 5) and twisted pairs (10 base T).
It is the known practice to provide a network element processor access to a local area network by means of a medium access unit (MAU). The MAU comprises electronics and associated connectors to allow the attachment of devices to the LAN medium comprising, e.g., a thin wire coaxial cable for 10 base 2. The MAU includes a coaxial transceiver and a BNC connector typically mounted on a printed board assembly (PBA) in a rack or shelf of electronic cards together comprising a network element.
Within the MAU is a coaxial transceiver comprising electronic circuitry that transmits and receives data. In order to connect to the LAN medium, a BNC "T" connector adapter is usually provided on the edge of the printed board assembly in close proximity to the MAU in order to keep the capacitance less than six picofarads as required by IEEE 802.3. The electrical "T" is the actual point of connecting the MAU to the network, i.e., where the signal is actually split out.
As known, synchronous optical network (SONET) equipment requires a single 10 base 2 connector visible to the user. SONET equipment also requires two redundant 10 base 2 MAUs connected to the same single LAN with only one MAU active at a time. There are both electrical and mechanical difficulties in implementing a design that meets both of these requirements.
Mechanical limitations of SONET equipment will not allow locating the traditional 10 base 2 connectors directly on the printed board assemblies which contain the MAU, as is recommended by IEEE 802.3, and which is the current state of the art. In other words, mechanical restrictions of SONET equipment do not allow placing a BNC "T" connector adapter at the printed board assembly edge.
Electrical limitations in meeting the IEEE 802.3 electrical specifications include minimum distance between 10 base 2 "nodes" (nodes meaning the usual BNC "T" connector adapters and the associated MAU and processor) of 0.5 meter, and the maximum capacitance of less than six picofarad between the MAU, located on the printed circuit board and the electrical "T" connection.
As far as can be determined, the state of the art is presently for the problem to be avoided by providing only one non-redundant MAU and Ethernet controller per LAN. However, this merely avoids the problem and does not lock to the future where we believe eventually it will be required to provide for two redundant Ethernet controllers per SONET network element, per local area network. This means that there will be two LANs per network element for a total of four Ethernet LAN controllers per network element. Note that redundant Ethernet controllers should be set up in a fail-safe fashion where each of two redundant main processing printed circuit boards has both an Ethernet controller and a MAU but only one main processor (and its Ethernet controller and MAU) can be active at a time.
Existing solutions will not support redundant MAUs on the same LAN. Moreover, only one external MAU/LAN connection on the chassis is typically allowed.
Therefore, it will be impossible to easily upgrade two redundant systems using existing solutions. The above future requirement is thus for two LAN connections since it is anticipated that redundancy will eventually be required.